(Nanowerk Spotlight) Peter Bøggild over at DTU just published an interesting opinion piece in Nature titled "The war on fake graphene".
The piece refers to a paper published in Advanced Materials ("The Worldwide Graphene Flake Production") that studied graphene purchased from 60 producers around the world.
This study used a systematic and reliable protocol that the authors developed to test graphene quality using optical microscopy (to identify flake size); atomic force microscopy (to measure the thickness of graphene stacks); Raman spectroscopy (which provides information on the structural integrity of the sample as well as indicates the presence of graphene oxide and reduced graphene oxide); X-ray photoelectron spectroscopy (to measure the carbon content to establish purity); and scanning electron microscopy and transmission electron microscopy to further characterize sample morphology.
The study's findings show unequivocally "that the quality of the graphene produced in the world today is rather poor, not optimal for most applications, and most companies are producing graphite microplatelets. This is possibly the main reason for the slow development of graphene applications, which usually require a customized solution in terms of graphene properties."
A conclusion that sounds even more damming is that "our extensive studies of graphene production worldwide indicate that there is almost no high quality graphene, as defined by ISO, in the market yet."
The team also points out that a large number of the samples on the market labelled as graphene are actually graphene oxide and reduced graphene oxide. Furthermore, carbon content analysis shows that in many cases there is substantial contamination of the samples and a large number of companies produce material a with low carbon content. Contamination has many possible sources but most likely, it arises from the chemicals used in the processes.
Contamination also affects the number of sp2 bonds. The study found that "crystalline graphene should have 100% sp2 bonds. However, we were not able to find, in any of the companies studied, a sample with more than 60% sp2 bonds."
Among the established methods for commercial graphene production, liquid-phase exfoliation (LPE) of graphite is one of the methods used most frequently. The mechanism behind LPE is based on the fact that graphite is a layered material and essentially can be seen as individual graphene crystals stacked one on top of each other.
The LPE process involves milling graphite into a powder, and separating the particles into tiny flakes by applying mechanical forces in a liquid. The graphene-containing flakes are then separated from the remaining material.